A valve control device is designed to move said valve between an open position and a closed position in order, depending on whether the valve is an inlet valve or an exhaust valve, either to admit fuel into a combustion chamber of the engine or to exhaust the burnt gases resulting from the combustion of the fuel.
A control device such as this generally comprises a valve actuating member that can move between two extreme positions corresponding to the valve open and valve closed positions, and an elastic system designed to cause the actuating member to oscillate between the two extreme positions. This elastic system generally comprises two antagonistic springs, namely a first spring acting on the actuating member in order to return it toward the extreme position corresponding to the open position and a second spring acting on the valve in order to return it to the closed position and therefore also to return the actuating member toward the extreme position corresponding to the closed position. The elastic system is in equilibrium when the actuating member is in a substantially central position between its extreme positions. The control device further comprises electromagnets associated with a control unit in order to attract the actuating member toward one or other of its extreme positions. The control unit is programmed to drive the electromagnets by employing a method of slaving the electromagnet supply current to an actuating member position.
The principle of operation of this control device is to use the elastic system to move the actuating member toward its extreme positions and to use each electromagnet to complete the movement of the actuating member toward one of its extreme positions and keep it in this extreme position.
Disturbances, such as a back pressure, excessive friction, electrical noise, etc. may impair the operation of the control device to such an extent that the actuating member escapes the attractive force exerted by one of the electromagnets attracting it toward the corresponding extreme position and tends to set off again toward its other extreme position. The control unit then powers the electromagnet in such a way as to increase the force of attraction and force the actuating member to return to the initially intended extreme position.
The power consumption of the electromagnets is then particularly high and the actuating member cannot be recovered which means that there is a risk that the valve will be uncontrollable for long enough to appreciably impair the correct operation of the engine.